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package com.oracle.truffle.sl.nodes.local;

import com.oracle.truffle.api.frame.VirtualFrame;
import com.oracle.truffle.api.profiles.BranchProfile;
import com.oracle.truffle.sl.nodes.SLExpressionNode;
import com.oracle.truffle.sl.runtime.SLNull;

/**
 * Reads a function argument. Arguments are passed in as an object array.
 * <p>
 * Arguments are not type-specialized. To ensure that repeated accesses within a method are
 * specialized and can, e.g., be accessed without unboxing, all arguments are loaded into local
 * variables {@link SLNodeFactory#addFormalParameter in the method prologue}.
 */
public class SLReadArgumentNode extends SLExpressionNode {

    /** The argument number, i.e., the index into the array of arguments. */
    private final int index;

    /**
     * Profiling information, collected by the interpreter, capturing whether the function was
     * called with fewer actual arguments than formal arguments.
     */
    private final BranchProfile outOfBoundsTaken = BranchProfile.create();

    public SLReadArgumentNode(int index) {
        this.index = index;
    }

    @Override
    public Object executeGeneric(VirtualFrame frame) {
        Object[] args = frame.getArguments();
        if (index < args.length) {
            return args[index];
        } else {
            /* In the interpreter, record profiling information that the branch was used. */
            outOfBoundsTaken.enter();
            /* Use the default null value. */
            return SLNull.SINGLETON;
        }
    }
}
